In order to analyze flue gases, for example, it is necessary to draw moisture laden gases into the sampling system. The moisture may be in the form of vapors or entrained liquid. The moisture in the gases, when it condenses, damages pumps and sensors interfering with the analysis. Since the analysis may be made at the location of a home furnace by furnace repairmen that carry all equipment to the location of testing, there exists the need for a simple, rugged piece of equipment for removing moisture from flue gases prior to analysis.
An example of a gas sampling device is disclosed in U.S. Pat. No. 5,018,395 entitled "Gas Sampling Device With Improved Mixed Flow Fan" assigned to the same assignee as this application.
Present solutions to the moisture problem are not satisfactory. One solution replaces a reciprocating pump with a mixed flow or centrifugal fan which can pass the condensate, however, this does not solve the problem of the moisture in the analyzer. Moreover, the suction that can be drawn by a centrifugal fan is typically limited to a 1 inch water column. Another solution is to pass the sample through a desiccant. The desiccant needs to be replaced hourly in currently used volumes, say, a liter per minute. The desiccant must then be reactivated by heating in an oven.
A complicated apparatus for condensing moisture from flue gas prior to analysis is disclosed in U.S. Pat. No. 3,680,388. Another apparatus for mechanically removing moisture from flue gases is disclosed in U.S. Pat. No. 5,240,486. In the latter device, flue gas is drawn in a tube and axially exhausted against a plate and then drawn into yet a larger volume before being exhausted to the analyzer.
It is an advantage of the moisture trap, according to this invention, that it is extremely simple to manufacture and use. The trap can be positioned in any orientation and still effectively trap moisture. Moreover, it is easily and quickly drained and returned to service.
Briefly, according to this invention, there is provided a moisture trap for removing moisture from sampled gases containing moisture in vapor and/or entrained liquid form. The trap comprises a small diameter elongate tubular conduit having a plug centrally positioned therein to prevent flow directly through the conduit. The conduit is provided with two radially directed holes, one positioned on each side of the plug and adjacent thereto, say, within 1/2 inch. A large diameter tube substantially concentric with the elongate tubular conduit is secured in place by plugs at each end thereof with openings therein for the elongate tubular conduit to pass therethrough. At least one of the plugs is provided with a second passage therethrough that can be stopped during sampling and unstopped for draining. The plug in the elongate tubular conduit is positioned to be approximately halfway between the plugs in the ends of the large diameter tube. Thus, during sampling, sample gases are drawn into one end of the elongate tubular conduit, exhausted radially into the space between the conduit and the tube such that vapor condenses on the inner surface of the tube and entrained liquid collects on the inner surface. The gas then re-enters the conduit on the other side of the plug and exhausts to the analyzer. Regardless of the orientation of the trap, it can accumulate liquid up to about 40% of its volume prior to requiring draining. Preferably, the radial holes in the elongate tubular conduit are positioned 180.degree. opposite to each other.